In a cellular communications network such as an LTE network, the uplink transmissions of a User Equipment, a UE, are scheduled by the eNodeB of the cell of the UE. The uplink transmissions of a UE are scheduled a certain amount of TTIs, Transmission Time Intervals, in advance. The uplink transmissions are usually scheduled by the eNodeB using some kind of metric or scheme, one example being the so called Proportional Fair, PF, metric.
The PF metric attempts to weight UEs with different long-term average channel conditions for each TTI and with the predicted channel conditions for the TTI that is being scheduled. However, scheduling uplink transmissions for UEs in one cell may cause interference in neighboring cells, which cannot be foreseen by the eNodeB in those cells in their scheduling, for example in a PF scheme in the eNodeB in those cells.
Besides scheduling UEs in a cell, the eNodeB of a cell also performs so called link adaptation of the UEs in the cell, which involves estimating the Signal to Noise and Interference Ratio, the SINR, when a transmission will be received by the eNodeB or the UEs (depending on the transmission direction, uplink or downlink), and the amount of information which can be transmitted reliably in future TTIs in view of the estimated SINR, a process which is usually referred to as link adaptation.
The scheduling decisions (uplink or downlink) taken by a scheme such as the PF metric are difficult to predict, and the interference that transmissions in one cell causes in neighboring cells is also difficult to predict, which causes a large “back-off” in the link adaptation.